yet another Cave thread ... add stalactites on an imported OBJ ... how

[ronthedon]

Holla,

I just started looking into TG again - I always try to despite work and the other annoying distraction called life .

I want to have a go at a cave with nice stalactites and -mites ... the approach I am trying this time is to have a general shape of the cave created externally and import it via the obj importer. 
I got normals sorted before the export and the walls of the cave have a certain thickness as well.

I am able to import the geo. However in the viewport all I am seeing is a hold-out looking grey object and on rendering I am getting weird polygonal "artifacts" ... i.e. I can see harsh polygons instead of a smooth surface - is there anything I am doing wrong here? (The same thing happens if I import a simple polygonal sphere).  The polygonal issue seems to be harsher in portions of the object closer to the camera.

Also I am trying to get the displacement working, which sort of works.  More specifically, I am getting something displaced but:
- results are quite random in the viewport (connecting a displacement shader-tree displaces, disconnecting it cancels it but then reconnecting the same shader tree doesn't displace it anymore until a restart)
- also do I need to "subdivide" my imported geo further in TG or is this done internally/"on rendertime" (in the viewport as well as the render)?
- and finally has anybody got some pointers on how to get stalactites?  I have searched the forums but haven't been able to find much on it.  I think the main problem is how they have different thicknesses along their length creating overhang-like-structures and such in themselves.   

thanks for any hints and help - much appreciated
cheers
Ron

[bobbystahr]

maybe upload the object and one of us will sort it?

[ronthedon]

thx for the reply bobbystahr.

happy to attach the cave geo. 

thanks for the help

[Oshyan]

First, there's another new-ish user struggling with potentially similar issues:
http://www.planetside.co.uk/forums/index.php/topic,19343.0.html
A lot of times it comes down to how an object is created, whether the source app uses triangles or polygons with more than 4 sides (n-gons), and other things like that. It's a general rule of thumb that you need to triangulate everything and have it at as high a polygon count as possible to effectively represent your modeler's shapes in TG or really any other app. It would help, though, to know what your modeling app is.

That being said I'm not sure your intentions for the workflow are really going to get you the results you want, due to some limitations in Terragen. Displacement quite simply does not work that well on imported objects. It *only* works at all with Raytrace Objects turned off, which we don't recommend because it's slower and render quality is lower. Even if you do render with RT Objects off, you need very high polygon counts in your source object to get decent results because Terragen does not subdivide imported geometry when displaced.

So the bottom line is I'd recommend considering another workflow, perhaps vector displacement, or some native TG displacement capability.

- Oshyan

[Dune]

Here's a very basic (blue node) setup you could use for your stalactites/mites. Just add it to your cave ceiling/floor, whether or not slope restricted, and do some finetuning.

[Oshyan]

I should also mention there have been many other attempts to tackle caves here in the forums, with actually a surprising amount of success with several *different* techniques. Few of them have the virtue of truly high degrees of control or "sculpting", but they at least create convincing caves, which in some cases you could add stalactites to as Ulco suggests. A search of the forums for "cave" ought to yield some interesting discussions.

- Oshyan

[ronthedon]

Thanks a lot for the replies and sorry for the delay in my reply..

@Oshyan:
my weapon of choice is Houdini.  I had read quite a few posts before and from memory one of them included your reply regarding  n-gones being a No-Go.  I had tried triangulation before as well and hadn't seen much of an improvement, but will use it from now on.
Thanks for the tip re turning of RT to get the displacement to show up.  I thought I was going crazy as I could see some sort of "displacement" but not at all what I expected.  Turning of RT at least got me the shapes I was expecting.
However u are right of course this approach isn't really giving me the results I was ignorantly expecting.  I did have some success though.  The technique could be used to quickly model a certain shape of a cave or whatever and then displace it as long as all of the original geo is covered up by displaced geometry i.e. if a certain existing cave needs to be rebuild.  Not exactly the procedural approach but could prove quite handy in the future for a quick and dirty job (the non raytracing renders would still need to be considered of course). 

I had read through a lot of the cave posts before posting mine.  And there is some really nice results in there.  Unfortunate I didn't find one that was helping me much with my approach.  The submarine thread however had a few great pointers in there.


@Dune: Thanks a lot for your setup. It proved quite handy for my testing purposes and was a lot better than the rudimentary displacement I was using before


cheers
Ron